The present disclosure relates to a power feeding apparatus, power receiving apparatus, wireless power feeding system, and method for supplying and receiving power in a noncontact (wireless) manner.
The electromagnetic induction method is known to supply power wirelessly.
In recent years, attention has been focused on wireless power feeding and charging systems using a method called the magnetic field resonance method that relies on the electromagnetic resonance phenomenon.
The currently popular noncontact feeding method based on the electromagnetic induction method requires that the source and destination of power (power receiving side) have to share a magnetic flux. For efficient power transmission, the source and destination of power have to be arranged extremely close to each other. Further, coupling alignment is also essential.
On the other hand, the noncontact power feeding method based on the electromagnetic resonance phenomenon is advantageous in that it allows for power transmission over a longer distance than the electromagnetic induction method thanks to the principle of the electromagnetic resonance phenomenon, and that the transmission efficiency does not degrade much even with somewhat poor alignment.
It should be noted that the electric field resonance method is another method based on the electromagnetic resonance phenomenon.
This wireless power feeding system based on the electromagnetic resonance phenomenon requires no alignment and permits extension of the power feeding distance. However, dynamic impedance control is required to make the most of this feature.
Japanese Patent Laid-Open No. Hei 10-163889 (hereinafter referred to as Patent Document 1) discloses an automatic impedance matching method that reliably matches input and output impedances even in the event of a change in output impedance of a power amplifier.
FIG. 1 is a block diagram illustrating a transmitter (power feeding device) using the automatic impedance control method disclosed in Patent Document 1.
The power feeding device (transmitter) shown in FIG. 1 includes a power amplifier 1, load impedance detector 2, matching circuit 3, antenna 4, AD converter 5, CPU 6, motor or relay drive circuit 7 and determination threshold setter 8.
In the power feeding device, the load impedance detector 2 is provided between the power amplifier 1 and antenna (load) 4. The matching circuit 3 is controlled by the detection signal from this load impedance detector 2, thus matching input and output impedances.
The load impedance detector 2 has been calibrated with the input and output impedances obtained when the output impedance of the power amplifier 1 and the load impedance are matched so that the load impedance detection signal voltage is the median value of the detection voltage.
The CPU 6 adapted to control the matching circuit 3 controls impedance matching by driving the motor or relay drive circuit 7 with a detection output. The impedance determination threshold of a matching control program executed by the CPU 6 is changed with change in output impedance of the power amplifier 1.
The impedance determination threshold is changed by the determination threshold setter 8.
FIG. 2 is a diagram illustrating an example of an existing transmitter disclosed in Patent Document 1.
In this case, no determination threshold setter is provided because there is no need to dynamically change optimal control.